Roman Concrete

Roman concrete, also called 'opus caementicium', was a material used in construction during the late Roman Republic. Roman concrete was based on a hydraulic-setting cement. Roman concrete is durable due to its incorporation of volcanic ash, which prevents cracks from spreading. By the middle of the 1st century, the material was used frequently, often brick-faced, although variations in aggregate allowed different arrangements of materials. Further innovative developments in the material, called the Concrete Revolution, contributed to structurally complicated forms, such as the Pantheon dome, the world's largest and oldest unreinforced concrete dome.

Roman concrete was normally faced with stone or brick, and interiors might be further decorated by stucco, fresco paintings, or thin slabs of fancy colored marbles. Made up of aggregate and cement, like modern concrete, it differed in that the aggregate pieces were typically far larger than in modern concrete, often amounting to rubble, and as a result it was laid rather than poured. Some Roman concretes were able to be set underwater, which was useful for bridges and other waterside construction.

It is uncertain when Roman concrete was developed, but it was clearly in widespread and customary use from about 150 BC; some scholars believe it was developed a century before that.

The Pantheon in Rome is an example of Roman concrete construction.